Question

In the upper atmosphere, nitrogen oxides react with one another; one such reaction is shown below. Using the component reactions, to find ∆Hrxn for the reaction of dinitrogen monoxide with nitrogen dioxide.

N2O + NO2 → 3 NO                 ∆Hrxn = ?

A: N2 + O2  → 2 NO                      ∆H° = +180.7 kJ

B: 2 NO + O2  → 2 NO2                ∆H° = -113.1 kJ

C: 2 N2O  → 2 N2  + O2                   ∆H° = -163.2 kJ

Answer 1

Lets number the reaction as 0, 1, 2, 3 from top to bottom

required reaction should be written in terms of other reaction

This is Hess Law

required reaction can be written as:

reaction 0 = +1 * (reaction 1) -0.5 * (reaction 2) +0.5 * (reaction 3)

So, deltaHo rxn for required reaction will be:

deltaHo rxn = +1 * deltaHo rxn(reaction 1) -0.5 * deltaHo rxn(reaction 2) +0.5 * deltaHo rxn(reaction 3)

= +1 * (180.7) -0.5 * (-113.1) +0.5 * (-163.2)

= 155.65 KJ

Answer: 155.65 KJ